If you wish to use the mailboxes for a specific domain name with an external mail server, you can easily do that by following these steps:

  1. Go to Domains, click the Domain Name.
  2. In the Web Site group click DNS Settings
  3. Now in the record type column, locate MX record, and click the respective link in the Host
  4. column on the left.
  5. Next, in the enter mail exchanger box, type the external mail server’s name and click OK.
  6. Click Up Level to return to the Domain Management screen.
  7. Now click Mail Accounts and Mail Settings.
  8. Clear the Activate mail service on domain check box and click OK.

Your domain will now use an external mail server.